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-   -   How to get a constant rotation speed? (http://www.cfd-online.com/Forums/cfx/20348-how-get-constant-rotation-speed.html)

Mangnan May 10, 2004 05:48

How to get a constant rotation speed?
 
Hi everyone:

I am now simulating a hydraulic turbine.And I use a rotation reference frame.I specified an angular velocity of 400 rpm which I assumed.So the angular velocity is not constant one.Then the fluid domain will accelerate aroud its aixs.Could anybody tell me how to get it?

Best Regards, Mangnan

Mangnan May 10, 2004 08:23

Re: How to get a constant rotation speed?
 
Hi everyone: Sorry I made a mistake in the message.Now I correct it. I am now simulating a hydraulic turbine.And I use a rotation reference frame.I specified an angular velocity of 400 rpm which I assumed.So the angular velocity is not constant one.Then the impeller will accelerate aroud its aixs.Could anybody tell me how to get it?

Best Regards, Mangnan


pp May 11, 2004 03:00

Re: How to get a constant rotation speed?
 
Did you have correct inlet condition at inlet section (inlet at spiral casing)?

Regards, pp

Mangnan May 11, 2004 09:52

Re: How to get a constant rotation speed?
 
Hi pp:

I know that to get the constant rotation speed I should adjust inlet condition.I am a freshman in hydraulic turbine simulating. I don't how to adjust it.When I correct the inlet condition,what should I depend on? Should I increase the inlet velocity(in my model I sspecified a inlet velocity)or decrease it? Some experts tell me I should adjust the inlet condition in order to get zero net torque.But the zero net torque is another problem which confuse me. Do you have another way to get the constant rotation speed?

Hope you and other experts give me some information about it.

Thanks

Mangnan

Mangnan May 12, 2004 03:59

Re: How to get a constant rotation speed?
 
Hi everyone:

I think my problem is a very fundamental one. So people who simulate the hydraulic turbine model would encounter such problem.How they solve it?

Best Regards, Mangnan

pp May 12, 2004 07:49

Re: How to get a constant rotation speed?
 
If you are simulating fluid flow through hydraulic machine (existing) then you should know runner angular velocity (rpm). Inlet conditions can taken by velocity inlet (if you knew volumetric flow rate) or total pressure which can be calculated. Hydraulic losses in penstock should be taken into account.

Hope I help you in some way.

Regards, pp

Mangnan May 13, 2004 00:47

How to get a constant rotation speed? Unsolved!
 
Hi pp:

Yes,you are right.I got the angular velocity from experiment. But we do not know whether the angular velocity is a constant one using in the simulation.Then the impeller will accelerate around its axis.And we can not trust the results from our simulation. What a confused problem!


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